Fix docs generation, PSR-12 type compliance (#790)

* Correct docs generation, fixes #774

* Standardise on unaliased int and bool types, as per PSR-12 section 2.5

src/FFMpeg/Media/Video.php

@@ -31,7 +31,7 @@ class Video extends AbstractVideo
      *
      * @param  TimeCode $at
      * @param  Dimension $dimension
-     * @param  integer $duration
+     * @param  int $duration
      * @return Gif
      */
     public function gif(TimeCode $at, Dimension $dimension, $duration = null)